The present invention relates to a continuous casting and hot rolling apparatus for the parallel production of different metal shapes, especially rods, wires and other rolled workpieces with a variety of cross sections.
Continuous casting and hot rolling have been used for the production of elongated strands of a variety of shapes from many different metals.
In general, the strand is produced at a flow-shaping unit, e.g. a continuous caster, from which an elongated strand is withdrawn, e.g. between a pair of pinch or squeeze rolls which can engage the strand from opposite sides.
The initial shape of the strand is imparted by the casting mold or by some other die or the like through which the metal is forced, e.g. by the extraction of the shaped strand at the discharge end or by the application of pressure at the inlet end.
The strand is rolled, usually after cutting into billets, to reduce its cross section, i.e. so as to make the workpiece thinner in at least one transverse dimension and to modify, if desired, the cross sectional shape. The rolling process may require a number of passes or passage through a succession of roll stands, or both, until the desired cross section is achieved.
With small cross section products, especially wire and rod, the processing becomes more cost intensive and more complex the number of reduction stages to which the strand must be subject becomes greater. To maintain a reasonable productivity, roll speeds must be increased continuously or stepwise from relatively slow speeds of the order of meters per minute to speeds of say 30 m/sec in the case of straight metal sections or shapes or 100 m/sec in the case of spooled metal wire, or more.
Efforts to increase these speeds have encountered barriers which are not easily overcome without increasing production and maintenance costs. Thus the operating speeds have limited productivity of lines for producing such products.
To overcome this drawback it has been proposed to utilize parallel production of metal shapes or at least parallel rolling techniques starting from the continuously cast product and running to the billets or bloom stage. These techniques, however, in spite of their potential for significant increase in the productivity of a processing line have not found major industrial application because of the complexity.
One of the problems faced in prior approaches is that when the rolls of the rolling line engage one of the strands or workpieces properly for cross section reduction, the rolls tend to jam with a second strand or workpiece, do not effectively roll the latter, create difficulties with respect to the rolling of the latter or make it impossible for the rolls to be fully effective with the second workpiece.
As a consequence, when billets have been rolled in a parallel production system, a split rolling process has been used. In this approach (see, for example, JP-A-60-130401), the rolled billet to be subdivided is reduced in cross section at a junction region and then split into two strands. The strands are then individually rotated through 90xc2x0 and rolled to reduce their cross sections along dimensions at right angles to the previous reduction and to the final thickness.
Utilizing this approach two or three workpieces can be split from an initial rolled billet.
It is also possible to form four steel strands by this general approach utilizing two successive splits with the same roll system and starting from the same kind of billet. For example, with this process a steel billet whose cross section may be 160 mmxc3x97160 mm from the heating furnace can be split into a multiplicity of workpieces and the rolled products can be obtained with an hourly production rate of for example 37 tons per hour.
This process must operate with roll speeds of the order of 3 m/min or 0.05 m/sec. In practice such roll speeds cannot be supported by many of the roll stands in use and as a result the product is replete with defects, has a large number of rejects and cannot be produced without detriment to the rolls in terms of overheating.
Furthermore, if one starts with a billet of 160 mmxc3x97160 mm in cross section to produce circular section rod or wire of a diameter of 8.5 mm for example, approximately 18 roll stands are required and the cost of the process line and operating same may be prohibitive. For such a system to be productive, the speed of the billet in the first mill stand must be about three times greater than the maximum continuous casting speed of such a billet and thus a continuous casting supply of the strand for this type of split strand rolling is impossible.
In German Patent Document 40 098 61A, a rolling line is described for the production of steel rod and in which the rolling line acts directly on a plurality of strands which derive from a continuously cast strip divided downstream of the continuous caster into the plurality of billets.
In JP 57-193205, a flat product is likewise subdivided into a multiplicity of billets which ultimately are separated from one another after having been transformed into rectangular portions located in diagonal relationship to one another and connected at corners of the respective cross section. In this case, the subdivision is not effected in conjunction with a continuous casting. Indeed, the flattened slab is initially subjected in a primarily rolling to a predetermined cross sectional reduction and reduction of thickness prior to the subdivision and is grooved in subsequent rollings before being split.
This latter approach is a discontinuous approach not unlikely the others described in the background hereto.
In EP 08 76 225, a method and hot rolling plant is described for the continuous production of bar, rod or wire which utilizes a continuous caster directly upstream of a rolling line and likewise produces individual slab-shaped continuous castings which are then transformed subsequently into respective products in the rod, wire or bar category by a slab splitting.
In the latter approach, a continuous caster serves as the source of the initial slab and is followed by a hot rolling line which ultimately produces the separate parallel-made products in the form of bar, rod or wire.
The rolling portion of the line comprises a first rolling unit for rolling the continuously cast slab with progressive reduction in cross section. The second rolling unit, with opposing grooved rolls, serves to produce a longitudinally grooved slab.
Upstream of the first rolling unit, EP 0 876 225 provides:
A continuous caster which continuously supplies the flat slab or bloom having a thickness less than 80 mm, preferably about 50 nm and adapted to be subdivided into the individual product units;
an induction furnace of tunnel shape, also referred to as an induction tunnel or as an equalizing furnace, for heating the advancing flat bloom or slab from the continuous caster to a hot rolling temperature;
an edging mill for the lateral rolling and having vertical rollers for shaping the advancing heated bloom or slab to impart to it an exact uniform width;
a splitting unit following the aforementioned second rolling unit for subdividing the advancing uniform-width bloom along longitudinal lines into a multiplicity of strips, bars or workpieces which can be shaped in parallel and can form the parallel-produced products bar rotators for rotating the resulting plurality or multiplicity of bars or strips by 90xc2x0; and
finishing roll units or stands with opposite angularly grooved rolls for the continuous production in parallel of a corresponding number of sectioned bars, rods or wires.
The drawbacks of that system, among others which have been mentioned with respect to the earlier systems, include the need for prerolling a flat slab or bloom. That prerolling step, which normally changes the rectangular shape of the continuously cast bloom to provided a somewhat oval or rhomboid shape and which requires both longitudinal and lateral rolling, it is complicated and expensive. This system, moreover, also may require the longitudinal division of the continuously cast strand to form the discrete blooms.
However, the system does have the advantage that the prerolling of the continuously case material before subdividing it into lengths, orients the fibers in the rolled material so that elongated fibers which are aligned in the longitudinal direction are formed, thereby improving the uniformity of the products which are obtained and the strength of the products.
It is the principal object of the present invention to provide an improved apparatus, plant or processing line, especially for the production of steel products, which enables metal rod or wire or structural shapes of a variety of cross sections of different size of shape to be produced by hot rolling at rolling speeds which are more effective than have been achievable heretofore, at high production rates and in an economical manner.
It is another object of the invention to provide an improved apparatus for the parallel production of steel rod and wire which eliminates drawbacks of the split strand method.
Still another object of this invention is to provide an apparatus which improved upon that described in EP 0 876 225 both in terms of the product rate and the types of products which can be produced and heat has the advantage of producing elongated workpieces of high strength.
These objects are achieved, in accordance with the invention, in a continuous casting and hot rolling apparatus for the parallel production of a multiplicity of different metal shapes, which comprise
a continuous caster having n flow shaping unit with a multistrand mold for casting respective continuous metal strands of different cross sections, where n is an even number but at least equal to 2 or  greater than 2;
an extractor including at least one pair of pinch rollers below the caster for drawing the strands from the molds;
a tunnel-shaped preheating induction furnace downstream of the extractor and traversed by the strands for heating the strands to hot-rolling temperature;
a hot-rolling line downstream of the induction furnace and comprising a multiplicity of roll stands successively engaging the strands and having rolls oriented for reducing cross sections of the strands in at least two different directions so that a width of 60 to 70 mm of each strands is reduced to about 12 mm with an increase of peripheral speed of the rolls at an inlet to the line of about 14 m/min to a peripheral speed of the rolls of about 12 m/sec at an outlet of the line;
at least n/2 universal rolling units downstream of the hot-rolling line and each comprised of 12 roll-pair groups oriented in isosceles triangle patterns and each traversed by two parallel and opposite ones of the strands for rolling same with a final peripheral roll speed of about 85 m/sec; and
loop control systems between the hot-rolling line and the apparatus upstream thereof and between the hot-rolling line and the units for compensating for speed variations between relatively upstream and downstream parts of the apparatus.
The flow shaping unit constituted by the continuous caster, of the invention, is capable of producing at least four mutually adjacent but geometrically different strands and small n can thus be an even number greater than 2, for example, 4, 6, 8, . . . . The reference to a flow-shaping unit or flow-shaping bore is intended to mean a bore in a continuous casting die which may be separated from the other bores thereof or may be a continuous casting die which itself is separate from other continuous casting dies but is capable of producing a continuous strand proximal to the other strands. It also may be some other flow-shaping passage and can be provided with pinch or squeezing rolls individual to the particular strand and the strand which emerges from the squeezing or pinch rolls can have round, oval or polygonal shapes. The shapes can be different from strand to strand or different from one group of strands to another group of strands.
The preheating furnace which has been described can be a tunnel shaped induction furnace of the type used in EP 0 876 225.
The loop control system or systems which have been described are intended to allow compensation between the upstream and downstream segments of the apparatus in terms of the speeds of the strands through them. The loop control system or systems is described in greater detail below.
In a preferred embodiment of the invention, in the hot rolling line, the rolling stands can provide six horizontal rolls and the mill stands are provided to permit rotation of the rolling directions through 90xc2x0 between successive passes or segments. The rolls of successive segments can thus be oriented at 90xc2x0 relative to one another, i.e. can be alternately horizontal and vertical rolls or can be provided such that the workpieces can be rotated through 90xc2x0 between successive passes. Advantageously, the mill stands of the hot rolling line include both horizontally and vertically oriented rolls and encompass at least a number of vertical roll pairs disposed in two parallel mutually adjacent rows, each of which forms a rolling channel which can be offset from one another by about half the axial spacing so that each row can include n/2 vertical roll pairs which are alternately used for the two rolling channels.
In an embodiment of the invention the rolling line can consist of six horizontal rolls which can alternate or be replaced by vertical rolls upon a rotation through 90xc2x0.
The system allows multiple rod, wire and structure shapes to be produced in a very compact apparatus.